1. Field of the Invention
The field of the invention relates generally to solid state motor actuators. More particularly, the invention relates to a single-piece multiple electrode conductor for piezoelectric solid state motor stacks.
2. Related Art
For decades electroexpansive materials have been employed in stacked structures for producing actuation used for fuel injection and valve control in diesel engines, for example. Commercially manufactured solid state motor stacks, or actuators, are produced using piezoelectric disks interleaved with metal foil electrodes. Application of high voltage, and resulting high peak current, power to alternately biased electrodes causes each of the piezoelectric disks to expand or axially distort. The additive deflection of the stacked disks is typically amplified by hydraulics to effectuate useful actuation.
An example of a conventional electromechanical actuator having an active element of electroexpansive material is found in U.S. Pat. No. 3,501,099 to Glendon M. Benson. Benson's 1970 patent is directed to both an actuation amplification structure and a method for manufacturing piezoelectric stacks. Sheets of ceramic material are rolled, compacted and punched into ceramic disks. After a cleaning process, the disks are stacked with alternate sets of continuous disk electrodes disposed between the ceramic disks. Alternate electrodes of the Benson structure are interconnected to one another to form a first group using straps. A second alternate group of electrodes is similarly interconnected. The stacks undergo a pressurized cold-welding process, followed by an elevated temperature and pressure bonding process after lead wire electrodes are connected to the two electrode groups. The stacks are poled by application of a DC voltage and then encapsulated with a plastic insulative cover prior to final mounting within a transducer housing.
Benson's above-described electrode structure represents a common serial approach to electrode interconnection. Another common interconnection scheme is the bus bar approach.
The bus bar scheme uses a common bar or wire to connect every other electrode in a parallel fashion. Each electrode includes a tab portion extending tangentially from a point on the circumference of the electrode. The tab is used to solder or weld the bus bar to the electrode. Conventionally, each stack uses two bus bars to connect the power supply leads to the two respective interconnected electrode groups.
Both of the above-discussed electrode interconnection structures suffer from various disadvantages. In Benson's strapped or chain structure current is drawn serially through the whole structure, thereby incurring unnecessary power losses. Additionally, Benson's chain structure makes assembly of ceramic disk/electrode stacks difficult. In contrast, structurally, the bus bar becomes somewhat rigid due to the soldering of the many tabs, thus, inhibiting stack actuation. Moreover, assembly and soldering of the bus bar structure requires many process steps. Additionally, potential high power losses may occur if the soldering joints are not of good quality.
The present invention overcomes the deficiencies of the conventional technology noted above.